SpringBoot JPA

Java Persistent API (Java持久化API)，Java标准，Hibernate框架是该标准典型实现。

JPA是用于对对象操作完成对DB操作。底层都是对JDBC技术的封装。

Spring Data模块功能提供了对JPA支持。在SpringBoot导入spring-boot-starter-data-jpa启动器。

  • 利用自动配置创建连接池对象（在JdbcTemplate过程的pom文件上导入)

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    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
        <version>2.1.2.RELEASE</version>
    </dependency>

  • 根据表定义实体类（需要定义与表的映射关系）

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    package cn.xdl.entity;
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.Id;
    import javax.persistence.Table;
    import java.io.Serializable;
    @Entity
    @Table(name="knowledge")
    public class Knowledge implements Serializable{
        @Id
        @Column(name="id")
        private Integer id;

        @Column(name="name")
        private String name;

        @Column(name="subject_id")
        private Integer subject_id;

        @Column(name="chapter_id")
        private Integer chapter_id;

        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public Integer getId() {
            return id;
        }
        public void setId(Integer id) {
            this.id = id;
        }
        public Integer getSubject_id() {
            return subject_id;
        }
        public void setSubject_id(Integer subject_id) {
            this.subject_id = subject_id;
        }
        public Integer getChapter_id() {
            return chapter_id;
        }
        public void setChapter_id(Integer chapter_id) {
            this.chapter_id = chapter_id;
        }
    }

  • 定义JPA Respository(Dao)接口,继承JpaRepository、CrudRepository等

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package cn.xdl.dao;
import cn.xdl.entity.Knowledge;
import org.springframework.data.jpa.repository.JpaRepository;
public interface KnowledgeDao extends JpaRepository<Knowledge, Integer>{

}

  • 定义启动类（@SpringBootApplication）

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    package cn.xdl;
    import cn.xdl.dao.KnowledgeDao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.ApplicationContext;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.PageRequest;
    import org.springframework.data.domain.Pageable;
    import org.springframework.data.domain.Sort;
    import java.util.List;
    @SpringBootApplication
    public class RunBoot {
      public static void main(String[] args) {
        ApplicationContext ac = SpringApplication.run(RunBoot.class, args);
        KnowledgeDao dao1 = ac.getBean(KnowledgeDao.class);
        List<Knowledge> list = dao1.findAll();
        list.forEach(know -> System.out.println(know.getId()+" "+know.getName()));

        //分页
        Sort sort = new Sort(Sort.Direction.ASC, "id");
        Pageable pageable = PageRequest.of(0, 3, sort);//page用索引从0开始
        Page<Knowledge> page = dao1.findAll(pageable);
        System.out.println("总页数:"+page.getTotalPages());
        List<Knowledge> list1 = page.getContent();
        list1.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
      }
    }

SpringBoot JPA扩展

  • 按规则定义方法名

    在上述的KnowledgeDao添加定义方法

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    import java.util.List;
    public interface KnowledgeDao extends JpaRepository<Knowledge, Integer>{

      public List<Knowledge> findByIdGreaterThan(int id);

      public List<Knowledge> findByNameLike(String name);

      public List<Knowledge> findBySubjectId(int subject_id);

    }

    在上述的启动类进行修改

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    package cn.xdl;
    import cn.xdl.dao.KnowledgeDao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.ApplicationContext;
    import java.util.List;
    @SpringBootApplication
    public class RunBoot {
      public static void main(String[] args) {
        ApplicationContext ac = SpringApplication.run(RunBoot.class, args);
        KnowledgeDao dao1 = ac.getBean(KnowledgeDao.class);
        //扩展操作
        List<Knowledge> list = dao1.findByIdGreaterThan(2);
        List<Knowledge> list1 = dao1.findByNameLike("%什么%");
        List<Knowledge> list2 = dao1.findBySubjectId(1);
        list.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
        list1.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
        list2.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
      }
    }

  • 定义SQL语句

    在上述的KnowledgeDao添加定义方法

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    package cn.xdl.dao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.data.jpa.repository.JpaRepository;
    import org.springframework.data.jpa.repository.Query;
    import org.springframework.data.repository.query.Param;
    import java.util.List;
    public interface KnowledgeDao extends JpaRepository<Knowledge, Integer>{
      @Query(nativeQuery=true,value="select * from knowledge where id>=:id")
      public List<Knowledge> findBySQL(@Param("id")int no);
    }

    在上述的启动类进行修改

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    package cn.xdl;
    import cn.xdl.dao.KnowledgeDao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.ApplicationContext;
    import java.util.List;
    @SpringBootApplication
    public class RunBoot {
      public static void main(String[] args) {
        ApplicationContext ac = SpringApplication.run(RunBoot.class, args);
        KnowledgeDao dao1 = ac.getBean(KnowledgeDao.class);
        //扩展操作
        List<Knowledge> list = dao1.findBySQL(2);
        list.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
      }
    }

  • 定义JPQL面向对象语句

    在上述的KnowledgeDao添加定义方法

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    package cn.xdl.dao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.data.jpa.repository.JpaRepository;
    import org.springframework.data.jpa.repository.Query;
    import org.springframework.data.repository.query.Param;
    import java.util.List;
    public interface KnowledgeDao extends JpaRepository<Knowledge, Integer>{
      //其中的Knowledge是类名
      @Query("from Knowledge where id>=:id")
      public List<Knowledge> findByJPQL(@Param("id")int no);
    }

    在上述的启动类进行修改

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    package cn.xdl;
    import cn.xdl.dao.KnowledgeDao;
    import cn.xdl.entity.Knowledge;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.ApplicationContext;
    import java.util.List;
    @SpringBootApplication
    public class RunBoot {
      public static void main(String[] args) {
        ApplicationContext ac = SpringApplication.run(RunBoot.class, args);
        KnowledgeDao dao1 = ac.getBean(KnowledgeDao.class);
        //扩展操作
        List<Knowledge> list = dao1.findByJPQL(3);
        list.forEach(know -> System.out.println(know.getId()+" "+know.getName()));
      }
    }